This invention relates to an articulator in which the movement of the row of teeth of a human mandible with respect to the row of teeth on a maxillary is transmitted to a mandibular cast so as to cause a movement of the latter identical with the movement of the former and in which the identical movement can be repeatedly reproduced.
In dentistry, it is necessary to observe the state of occlusion of molars in motion in an intraoral cavity. However it is extremely difficult to make an accurate observation of the state of occlusion. For this observation an articulator is usually used. Conventional articulators first make a recording of a portion of the condyle paths, and then form the corresponding condyle paths indirectly on the articulator based on the recorded condyle paths. This operation is very difficult and requires a lot of time. Further more, as the glenoid fossa is concave, the condyle paths must also be formed by curved lines. However, heretofore, the paths have been formed by straight lines and angles, since it is difficult to form the condyle paths by curved lines.
Japanese Laid Open Patent Application No. 37,944/1973, which is an application of the present Applicant, provided an articulator which partly solves the above problem. However in this articulator all of the members of the articulator are suspended by suspending strings. Accordingly the row of teeth on the maxillary is easily moved, since the entire weight of the apparatus can swing on the strings, so that the condyle paths cannot be formed very exactly making it difficult to reproduce the movement exactly. Moreover, because most of the weight of the articulator driven by the mandible is supported by the mandible, so that natural movement is made difficult, thus making accurate reproduction of the movement difficult.
It is an object of the invention to provide an articulator for observing the occlusion, in which the movement of the row of teeth on the mandible with respect to the row of teeth on the maxillary in the intraoral cavity is accurately and directly transmitted to a mandibular cast so as to cause identical movement in the latter, and which can reproduce repeatedly the movement as it was at a desired time.
It is another object of the invention to provide an articulator which can be easily operated and which requires only a small force from the mandible of the patient.
The present invention is an articulator for observing the occlusion between a mandible and a maxillary, which comprises a frame, a first adjustable bite fork mounted on the frame for holding and positioning the maxillary, a second adjustable bite fork for holding the mandible, a mandibular cast adjustably mounted on the frame, a maxillary opposed to the mandibular cast, a link means for transmitting the exact movement of the mandible to the mandibular cast, and machining means which grinds solid material disposed on the frame and which is rigidly connected to the mandibular cast. When all the possible movements of the mandible are brought about, condyle paths are formed in the solid material. Every possible movement of the mandible is reproduced in the movement of the mandibular cast by tracing the formed condyle paths.
The link means comprises a beam fixed to the frame, two movable plates facing each other, three parallel rods which are connected to the plates at the ends thereof by means of ball joints, and positioned at the apexes of an isosceles triangle with the rods being parallel to the beam, two first arm plates which are rotatably mounted on two of the three horizontally parallel rods at one of their respective ends, and which are slidable on the two rods in the longitudinal direction, and two second arm plates which are mounted on the beam at one of their ends and are prevented from sliding on the beam in the longitudinal direction with other ends of each one of the first arm plates and second arm plates being rotatably connected to each other. One of the facing plates is connected to the second adjustable bite fork, and the other of the facing plates is connected to the mandibular cast.
According to an embodiment of the invention, the link means is enclosed in a box disposed on the lower portion of the frame.
The weight of the mandibular cast, the machining means and the movable members of the link means is balanced by springs so they are movable by small force.
The machining means are preferably vertically disposed burrs driven by a motor. The positional relationship of the mandibular cast with respect to the tip of the burrs is the same as that of the mandible with respect to the condyle points. The solid material is preferably made of plaster particles bonded with polymers and has a low contractibility and of high machinability.
As above described, the most outstanding feature of the articulator of the present invention is that the mandibular movements of the patient form the condyle paths i.e. the curvature of the functional glenoid fossa, directly. Consequently, it is not necessary to measure the terminal hinge or various condyle angles. The operation is very simple and is completed in a short time. Above all the exact mandibular movement of the patient can be reproduced.